The present invention relates to a liquid crystal display for displaying an image to be visible for a viewer.
JP-A-8-015697 discloses that a color toner adjuster for adjusting a color tone of a light as a back light generated by a fluorescent light source is arranged between the fluorescent light source and a light guide for distributing constantly the back light over a liquid crystal display panel in a STN type liquid crystal display unit.
JP-A-2000-206544 discloses that an unevenness in an image to be displayed is restrained by preventing a liquid crystal from being contaminated by a liquid crystal cell sealing resin before being cured, in an active matrix in-plain switching mode liquid crystal display in which a pair of comb-shaped electrodes is used.
JP-A-2000-19543 discloses a method for restraining an unevenness in an image caused by an error in dimension of electrodes.
JP-A-10-170923 discloses that a twisted connection between a liquid crystal molecule and a directing layer surface at the interface therebetween is made weak to decrease the unevenness in the image caused by an error in distance between substrates between which the liquid crystal is arranged.
An object of the present invention is to provide a liquid crystal display for displaying an image to be visible for a viewer, in which a so-called blue fog phenomenon is restrained even when a brightness of the image is low. The lower a voltage for controlling an orientation of a liquid crystal is, the higher a permeability of the liquid crystal for a blue color light is. When the voltage for controlling the orientation of the liquid crystal is close to a threshold voltage of the liquid crystal so that a transmittance of the liquid crystal for the light is low, that is, a brightness of the display is low, a light of wave-length 400-440 nm as a blue color light is more effectively transmitted through the liquid crystal in comparison with another light of wave-length not less than 440 nm, and a difference in brightness and a difference in color can be clearly visible. Therefore, the so-called blue fog phenomenon occurs.
According to the invention, a liquid crystal display for displaying an image to be visible for a viewer, comprises, a liquid crystal, a pair of electrodes for controlling a molecular orientation of at least a part of the liquid crystal in accordance with an electric field between the electrodes, a light source for generating a light to be transmitted through the liquid crystal to the viewer, a pair of first and second polarizer plates, the first polarizer plate being arranged between the liquid crystal and the light source, and the second polarizer plate being arranged between the liquid crystal and the viewer, and a band-pass filter for absorbing a component of the light, a wave-length of which component is not more than 440 nm, and the band-pass filter being arranged between the light source and the viewer.
Since the band-pass filter for absorbing the component of the light, a wave-length of which component is not more than 440 nm, is arranged between the light source and the viewer, when the voltage for controlling the molecular orientation of the liquid crystal is close to a threshold voltage of the liquid crystal so that a transmittance of the liquid crystal for the light is low, that is, a brightness of the display is low, and a light of wave-length 400-440 nm as a blue color light is more effectively transmitted through the liquid crystal in comparison with another light of wave-length not less than 440 nm, the light of wave-length 400-440 nm as the blue color light is restrained from reaching the viewer, so that the so-called blue fog phenomenon is prevented.
In order to generate correctly another color visible for the viewer while the so-called blue fog phenomenon is prevented, it is preferable that a transmittance of the band-pass filter for the component of wave-length not more than 440 nm is smaller than a transmittance of the band-pass filter for another component of the light, a wave-length of which another component is not less than 450 nm, that a transmittance of the band-pass filter for the component of wave-length 400-440 nm is smaller than a transmittance of the band-pass filter for another component of the light, a wave-length of which another component is not less than 450 nm, that a transmittance of the band-pass filter decreases in accordance with a decrease of a wave-length of a light to be transmitted through the band-pass filter when the wave-length of the light to be transmitted through the band-pass filter is less than 450 nm, and/or that a transmittance of the band-pass filter decreases in accordance with a decrease of a wave-length of a light to be transmitted through the band-pass filter when the wave-length of the light to be transmitted through the band-pass filter is 400-440 nm.
The band-pass filter may be arranged between the light source and a light guide for guiding the light from the light source to the liquid crystal to distribute the light evenly over the liquid crystal. When a diffusing plate for distributing constantly the light over the liquid crystal is arranged between the light guide and the liquid crystal, and the band-pass filter may be arranged between the diffusing plate and the light guide. The band-pass filter may be arranged on the light source. The band-pass filter may be arranged on the light guide. When the liquid crystal display comprises a pair of first and second substrates being at least partially transparent and the liquid crystal is arranged between the first and second substrates, the band-pass filter may be arranged on at least one of the first and second substrates. The band-pass filter may be arranged on at least one of the first and second polarizer plates. The band-pass filter is preferably arranged between the light source and the liquid crystal.
When the liquid crystal display comprises a color filter including a portion for transmitting therethrough a blue light, the portion includes an agent for absorbing the component of the light as the band-pass filter.
The band-pass filter may be a stack of layers. The band-pass filter may be a polymer for absorbing the component of the light. The band-pass filter may be a resin including an agent for absorbing the component of the light.
The light source may include a fluorescent substance for generating the light. The liquid crystal and the pair of first and second polarizer plates may form a normally close type liquid crystal display unit. A direction in which the light is transmitted in the liquid crystal may be prevented from being parallel to a direction in which the electric field is generated or may be transverse with respect to the direction in which the electric field is generated. The liquid crystal and the pair of first and second polarizer plates may form a super twisted nematic type liquid crystal display unit.